Piston for rotary piston machines and means for its manufacture

ABSTRACT

A multi-apex fluid-cooled piston is provided with cavities at the apices into which coolant is fed from one of the piston faces and from which the coolant is conducted away towards the other face of the piston. In the region of the point of entry of the inlet passage into the outlet passage, the outlet passage is wider and spaced away from the radially outermost defining wall of the outlet passage. A tool is also provided for producing this multi-apex piston.

, 1 States Patent Steinwart et a1.

[ Sept, 17, 1974 PISTON FOR ROTARY PISTON MACHINES AND MEANS FOR ITS MANUFACTURE Inventors: Johannes Steinwart, Bad

Friedrichshall II; Max Rut, Oberisesheim, both of Germany Assignees: Audi NSU Auto Union Aktiengesellschaft, Neckarsulm/Wurttemberg; Wankel GmbH, Lindau/Bodensee, both of, Germany Filed: Dec. 15, 1972 Appl. No.: 315,581

Foreign Application Priority Data Dec. 24, 1971 Germany 2164646 US. Cl 418/91, 123/801, 164/137,

164/340 Int. CL... F01c 21/06, B22d 33/04, FO4c 29/04 Field of Search 418/61 A, 91; 123/801 [56] References Cited UNITED STATES PATENTS 3,269,370 8/1966 Paschke et al 418/91 3,333,763 8/1967 Jungbluth et al. 418/91 Primary Examiner-John J. Vrablik Attorney, Agent, or Firm-Kane, Dalsimer, Kane, Sullivan and Kurucz [5 7 ABSTRACT A multi-apex fluid-cooled piston is provided with cavities at the apices into which coolant is fed from one of the piston faces and from which the coolant is conducted away towards the other face of the piston. In the region of the point of entry of the inlet passage into the outlet passage, the outlet passage is wider and spaced away from the radially outermost defining wall of the outlet passage. A tool is also provided for producing this multi-apex piston.

3 Claims, 7 Drawing Figures PMMEUSEP I 7 mm 11836; 29A

sum 1 W a PISTON FOR ROTARY PISTON MACHINES AND MEANS FOR ITS MANUFACTURE BACKGROUND OF THE INVENTION This invention relates to a piston for rotary piston machines. It is concerned in particular with a multiapex fluid-cooled piston, for example, of light alloy, of trochoidal type, which is provided in the region of its apices with cavities to which the coolant is fed from one face of the piston and from which the coolant is conducted away towards the other face of the piston. The invention is also concerned with means for manufacturing such a piston.

In the known pistons of the above-mentioned kind the cavitles can only be formed with the aid of sand cores which are subsequently destroyed. This method of manufacture is expensive and is not well suited to large-volume production.

SUMMARY OF THE INVENTION The aim of the invention is to provide a piston of which the cavities are arranged to allow manufacture by die-casting, yet without detracting from the flow of the coolant through the cavities from the one face of the piston to the other under the action of the alternating centrifugal acceleration forces.

According to the invention we propose that the invididual cavities in the piston should each be formed by two converging passages of which the one serves as an inlet passage and starts from the one face of the piston and opens into the other passage which serves as the outlet passage and leads to the other face of the piston, and in the region of the point of entry the inlet passage into the outlet passage the outlet passage is wider in a circumferential direction than the inlet passage, and furthermore this point of entry lies at a point in the outlet passage which is spaced away from the radially outermost defining wall of the outlet passage.

This allows each cavity to be produced by two mutually engaging core portions which, after casting, can be withdrawn inward along inclined radial paths in axially opposite directions. By the arrangement defined for the meeting point between the inlet passage and the outlet passage we largely prevent any reverse flow of coolant back through the inlet passage when negative, i.e., substantially radially inwardly directed, centrifugal acceleration forces arise. On the contrary the coolant, which is delivered from the inlet passage to the outlet passage by positive centrifugal forces (i.e., those which are directed radially outward) is pumped away almost entirely through the outlet passage by the action of negative forces. This effect can be improved still further if the radially outermost defining wall of the outlet passage extends in a direction which is inclined with respect to the axis of rotation of the piston in such a way that the point of its greatest radial distance from the axis is displaced from the point of entry of the inlet passage in a direction towards that face of the piston into which the outlet passage opens. The coolant guided through the inlet passage thus collects first at this outermost point of the outlet passage and when on further rotation of the piston radially inwardly directed acceleration forces arise, the coolant which is consequently radially inwardly urged cannot flow back into the inlet passage.

The inlet passages may start from an annular groove which is provided in the piston at its one face, and the outlet passages could lead into an annular groove which is provided in the piston at its other face and which is interrupted between adjacent apices of the piston by webs. These annular grooves serve to cool the faces of the piston in the region of the so-called axial seals, i.e., the annular seals that are provided in the end faces of the piston. The webs which interrupt the annular groove at the outlet face of the piston have the purpose of urging radially inwards the coolant which emerges from the individual cavities of the piston.

The piston can be made by dlie-casting, multipart cores being used to produce the cavities as is known in the production of reciprocating pistons. A tool according to the invention for producing a piston comprises two cores which are capable of being withdrawn in mutually opposed directions, one of the cores having a hub and a number of movable core portions arranged around it, equal to the number of apices for forming the inlet passages and core portions for forming the inner surface of the piston between the inlet passages, and the other core likewise comprising a hub and a similar number of movable core portions arranged around it, equal to the number of apices, for forming the outlet passages and core portions for forming the inner surface of the piston between the outlet passages. The engagement between the core portions of each core can be arranged so that after the hub has been withdrawn first the one set of movable core portions can be withdrawn and then the other core portions. One of the hubs may carry, or itself form, a core for forming the central bearing opening of the piston.

Alternatively a core with only a single hub may be used, the hub having the appropriate number of movable core portions on it for forming the outlet passages and also the appropriate number of core portions for forming the inner surface of the piston between the outlet passages. The inlet passages are formed later by drilling them in the casting.

BRIEF DESCRIPTION OF THE DRAWINGS Further details and features of the invention are re vealed by the following description in conjunction with the accompanying drawings, in which is illustrated an embodiment of the piston according to the invention by way of example, as well as a die-casting mould.

In the drawings:

FIG. I is a longitudinal section through the piston along the line l-]l of FIG. 2;

FIG. 2 is a view looking in the direction of the arrow A in FIG. 1;

FIG. 3 is a view in the direction of the arrow B in FIG.

FIG. 4 is a longitudinal section through the piston and the associated mould and cores for casting it;

FIG. 4a is a partial section along the line Ark-Au in FIG. 4;

FIG. 6 is a section along the line l6-6 of FIG. 4.

DETAILED DESCRlPTION We will describe first the piston il illustrated in FIGS. II to 3, and in the example illustrated this is formed as a light alloy casting and has three apices 2 and a central bearing opening 3. The piston II is provided in the regions of the apices 2 with cavities to which a coolant is fed from the one face of the piston and from which the FIG. 5 is a section along the line 5-5 in FIG. 4; and

coolant is led away towards the other face of the piston. This movement of the coolant through the cavities is achieved in a manner which is known in itself by the centrifugal acceleration forces which vary in direction as the piston rotates on an eccentric on a rotating eccentric-carrying shaft in the usual manner of rotary piston machine. This effect is described in detail in German Pat. Specification No. 1,223,610.

In the piston according to the invention the individual cavities in the piston are each formed by two converging passages 4 and 5 which are free of undercuts and of which the passage 4 serves as an inlet passage and starts from the one face 6 of the piston and opens into the other passage 5. This other passage 5 serves as the outlet passage and leads to the other face 7 of the piston. The coolant is thus urged radially outwards through the inlet passage 4 and into the outlet passage 5 by the radially outwardly acting centrifugal forces and it subsequently flows radially inward through the outlet passage 5 under the action of radially inwardly directed acceleration forces, moving to the left in FIG. 1 from where it flows out of the piston. So as to prevent the coolant flowing back through the inlet passage 4 when the radially inwardly directed forces arise, the circumferential width of the outlet passage 5 is greater than that of the inlet passage 4 in the region where the inlet passage 4 enters it, and in addition the point of entry of the inlet passage 4 is spaced away from radially outermost defining wall 8 of the outlet passage 5. This is shown particularly clearly in FIG. 2. The coolant emerging from the inlet passage 4 is flung against the outermost defining wall 8 of the outlet passage 5 and on further rotation of the piston it flows around the entry point of the passage 4 without flowing back into that passage 4. Also, to prevent such return flow of the coolant into the inlet passage 4 at the moment during which the centrifugal forces acting on the piston are directed wholly radially inward, the the radially outermost wall 8 of the outlet passage 5 extends in a direction which is inclined with respect to the axis of rotation of the piston, as shown in FIG. 1. The point 9 of maximum radial distance from the axis of rotation of the piston is axially displaced away from the point of entry of the inlet passage 4 in a direction towards the face 7 of the piston so that the coolant which has accumulated in this region under the action of the previous radially outwardly acting forces is not flung back into the inlet passage 4 but is flung against the radially innermost defining wall 10 of the outlet passage 5 and is guided away laterally.

The inlet passages 4 start from an annular groove 11 which is provided in the piston close to the face 6. The coolant flowing into this groove 11 acts to cool the piston in the region where the so-called axial seals (formed in the face 6 but not shown) are present. In a corresponding manner an annular groove 12 is provided in the other face of the piston, into which the outlet passages 5 open. This groove 12 is interrupted between adjacent apices of the piston by web 13 (FIG. 2). The coolant passing from the individual outlet passages 5 into the groove 12 is diverted radially inward at tHe webs 13 and is led away into the end portions of the housing in a known manner by appropriately placing passages.

We now refer to FIGS. 4 to 6 in which is illustrated a mould from producing the piston by die-casting. This mould comprises an external mould portion made up,

for example, of three parts 14, 14a and 14b which each extend from one apex to the next. This outer mould does not however form any part of the invention. To form the inner cavities of the piston there are provided two cores l5 and 16 which are capable of being withdrawn axially in opposite directions. The core 15 has a hub 22 and three portions 17 of which projections 18 form the inlet passages 4. The inner surface of the piston between the passages 4 is formed by three further core portions 19 on the hub 22. The portions 17 and 19 have flat faces 20 and 21, respectively, which engage six faces of the hub 22, which is in the shape of a frus- .tum of a pyramid. The core portions 17 and 19 are urged radially outward by the hub 22 in their operative position for casting, in which they engage a coreguiding bush 23.

The core 16 similarly contains three core portions 24 which are provided with extensions 25 for forming the outlet passages 5. Between these portions 24 there are portions 26 for forming the inner surface of the piston between the adjacent outlet passages. The portions 24 and 26 have flat faces 27 and 28, respectively, by which they engage the six faces of a hub 29 and they are urged radially outward by this hub against a core-guiding bush 30. The hub 29 has an extension 31 which defines the central bearing opening 3 of the piston. After casting the hubs 22 and 29 are withdrawn respectively to the right and to the left in FIG. 1 and then the core portions 17 and 24 are withdrawn in the direction of the arrow a after which the remaining core portions 19 and 26 can be withdrawn in the direction of the arrows b. After the outer mould parts 14, 14a and 14b have been opened up the casting is free and can be removed to undergo mechining to produce a finished piston.

In a modification, not illustrated, the right-hand hub 22 and its associated core portions 17 and 21 can be omitted, and only the outlet passages 5 are formed by casting. The inlet passages are formed by subsequent machining of the casting, the annular groove 11 also being machined. The passages are formed by drilling, after the groove 11 has been turned.

What we claim is:

l. A multi-apex piston for rotary piston machines of the trochoidal type provided with cavities in the region of the apices, to which coolant is supplied from the one face of the piston and from which the coolant is led away towards the other face of the piston, in which the individual cavities of the piston are each formed exclusively by two converging passages free of undercuts, of which the one passage serves as an inlet passage and starts from the one face of the piston and opens into the other passage which serves as an outlet passage and leads to the other face of the piston, and in the region of entry of the inlet passage into the outlet passage the outlet passage is circumferentially wider than the inlet passage, and moveover the point of entry of the inlet passage into the outlet passage is spaced away from the radially outermost defining wall of the outlet passage, and the outlet passage tapers slightly from the outermost defining wall to the other face of the piston.

2. A piston according to claim 1 in which the radially outermost defining wall of the outlet passage extends in a direction which is inclined to the axis of rotation of the piston in such a way that the point of its greatest radial distance from the axis is axially displaced away from the point of entry of the inlet passage in a direction towards the said other face of the piston.

3,836,294 6 3. A piston according to claim 1 in which each of the is provided in the piston near its said other face which inlet passages start from an annular groove provided in is interrupted by webs between adjacent apices of the the piston near to the said one face of it and in which piston. the outlet passages open into an annular groove which 

1. A multi-apex piston for rotary piston machines of the trochoidal type provided with cavities in the region of the apices, to which coolant is supplied from the one face of the piston and from which the coolant is led away towards the other face of the piston, in which the individual cavities of the piston are each formed exclusively by two converging passages free of undercuts, of which the one passage serves as an inlet passage and starts from the one face of the piston and opens into the other passage which serves as an outlet passage and leads to the other face of the piston, and in the region of entry of the inlet passage into the outlet passage the outlet passage is circumferentially wider than the inlet passage, and moveover the point of entry of the inlet passage into the outlet passage is spaced away from the radially outermost defining wall of the outlet passage, and the outlet passage tapers slightly from the outermost defining wall to the other face of the piston.
 2. A piston according to claim 1 in which the radially outermost defining wall of the outlet passage extends in a direction which is inclined to the axis of rotation of the piston in such a way that the point of its greatest radial distance from the axis is axially displaced away from the point of entry of the inlet passage in a direction towards the said other face of the piston.
 3. A piston according to claim 1 in which each of the inlet passages start from an annular groove provided in the piston near to the said one face of it and in which the outlet passages open into an annular groove which is provided in the piston near its said other face which is interrupted by webs between adjacent apices of the piston. 